A databases model shows the logical structure of databases, including the relationships and constraints that determine how data can be stored and accessed. Individual database models are designed based on the rules and concepts of whichever broader data model the designers adopt.
Types of Database Models
1- Hierarchical Database Model
This is the oldest form of database. This data model organizes the data in the tree structure (for example employee records might be grouped under a record describing the departments in which employees work)
In this model, a database record is a tree that consists of one or more groupings of fields called segments, which make up the individual nodes of the tree. This model use one-to-many relationship
the advantage of this data is that Data access is quite predictable in structure and retrieval and updates can be highly optimized by a DBMS. But the bad thing in it is that the link is permanently established and cannot be modified which makes this model rigid.
2- Network Database Model
The Network database model was developed as an alternative to the hierarchical database. This model expands on the hierarchical model by providing multiple paths among segments (e.g. employee records might be linked on one hand to employees’ departments and on the other hand to their supervisors—that is, other employees). so, this model allows one-to-one, one-to-many and many-to-many relationships
Supporting multiple paths in the data structure eliminates some of the drawbacks of؛ It can be quite complicated to maintain all the links.
3- Relational Database Model
In which all data are represented in simple tabular form. The key differences between previous database models and relational database model are in terms of flexibility؛ Provides flexibility that allows changes to the database structure to be easily accommodated. It facilitates multiple views of the same database for different users.
A relational database represents all data in the database as simple two-dimensional tables called relations. Each row of a relational table, called tuple, represents a data entity with columns of the table representing attributes(fields). The allowable values for these attributes are called the domain.
Each row in a relational table must have a unique primary key and also has some secondary keys which correspond with primary keys in other tables.
4- Object-Oriented Database Model
The relational database model has a wide variety of applications. However, it does not easily support the distribution of one database across a number of servers. Due to this, the object-oriented database management system was developed.
In these databases, the users can define own data access methods, the representation of data and the method of manipulating it. An object-oriented database stores and maintains objects.
5- Entity-relationship model
This model captures the relationships between real-world entities much like the network model, but it isn’t as directly tied to the physical structure of the database. Instead, it’s often used for designing a database conceptually.
Here, the people, places, and things about which data points are stored are referred to as entities, each of which has certain attributes that together make up their domain. The cardinality, or relationships between entities, are mapped as well.
Integrity is a major database issue. In general, integrity refers to maintaining the correctness and consistency of the data. Some integrity checking is made possible by specifying the data type of an item. For example, if an identification number is specified to be nine digits, the DBMS may reject an update attempting to assign a value with more or fewer digits or one including an alphabetic character.
Another type of integrity, known as referential integrity, requires that an entity referenced by the data for some other entity must itself exist in the database. For example, if an airline reservation is requested for a particular flight number, then the flight referenced by that number must actually exist.